# std::chrono::operator<<(std::chrono::weekday)

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< cpp‎ | chrono‎ | weekday

Defined in header `<chrono>` |  |
template< class CharT, class Traits > std::basic_ostream<CharT, Traits>& operator<<( std::basic_ostream<CharT, Traits>& os, const std::chrono::weekday& wd ); |  | (since C++20)

If !wd.ok(), inserts wd.c_encoding() followed by " is not a valid weekday" into os. Otherwise, forms a std::basic_string<CharT> s consisting of the abbreviated weekday name for the weekday represented by wd, determined using the locale associated with os, and inserts s into os.

Equivalent to

return os << (wd.ok() ?
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{:L%a}"), wd) :
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{} is not a valid weekday"),
wd.c_encoding()));

where STATICALLY_WIDEN<CharT>("...") is "..." if `CharT` is char, and L"..." if `CharT` is wchar_t.

### Return value

os

### Example

| This section is incomplete Reason: no example

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P2372R3 | C++20 | the given locale was used by default | `L` is needed to use the given locale

### See also

format (C++20) | stores formatted representation of the arguments in a new string (function template)
std::formatter<std::chrono::weekday> (C++20) | formatting support for `weekday` (class template specialization)

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